1. Field of the Invention
The present invention relates to an improvement in propulsion power systems for turbofan jet engines for aircraft and more particularly, but not by way of limitation, to an independently mounted translatable air inlet system for a turbofan aircraft jet engine.
2. Description of the Prior Art
The function of a nacelle for a turbofan jet engine for an aircraft is generally considered to be twofold. The nacelle must provide an air flow to the air intake of the engine with minimal disturbance for a variety of flight conditions which include high incidence, gusts, and the like. Also, the exterior profile of the nacelle should minimize aerodynamic drag, subject to constraints fail imposed by major engine components such as the accessories gearbox.
Considering the exterior profile of a nacelle, the skin friction component of the overall profile drag is directly affected by discontinuities on the outer surface. While the ideal would be for a smooth, uninterrupted outer surface, this ideal is compromised in nacelles previously proposed by the various breaks in the outer skin which arise due to split lines between the serially arranged nacelle components and to the doors and panels required to gain access to the equipment housed within.
While efforts have been made in the past to minimize discontinuities of the outer skin and to improve the exterior profile of a nacelle, it has been found that other aspects of nacelle construction may have a very significant effect upon the overall operation of the propulsion power system. Traditional turbofan air inlet and cowling arrangements of a nacelle consist of an inlet cowl secured to the fan casing of the engine with a direct bolted flange. This inlet cowl forms an internal aerodynamic source, which conditions the air for delivery to the engine fan and to the inlet of the engine itself It also forms the initial external aerodynamic surface, which smooths the airflow around the nacelle and systems associated with the fan case of the aircraft jet engine. An additional set of cowls form the remainder of the external aerodynamic source over the fan casing of the engine, and are split into two xe2x80x9cCxe2x80x9d shapes that are hinged from the aircraft pylon structure. Thus, a traditional high bypass turbofan aircraft engine nacelle system is considered to comprise an inlet cowl secured to the fan case of the engine, two C-shaped fan cowl portions secured to a pylon structure, a bifurcated thrust reverser portion secured to the engine body, and an exhaust cone and nozzle.
This traditional arrangement has three undesired effects which become increasingly more punitive as the size of the engine and resultant fan size increases. The first effect is the imposition of a bending moment on the fan case of the engine at certain flight conditions, particularly at take-off rotation, thereby leading to out-of-round distortion of the body of the engine giving rise to irregular blade tip rubs and loss of performance of the engine. The second effect is the need of increasingly stiff, and hence heavy, fan cowls to cope with intrinsic weight and wind gust loads when opened for required maintenance. The third effect is the reliance on the bolted attachment flange between the engine and the inlet cowl to retain the inlet cowl in the nacelle structure following a blade-out event.
The following patents, while of interest in the general field to which the present invention pertains, do not disclose the particular aspects of the invention that are of significant interest.
U.S. Pat. No. 5,609,313 issued on Mar. 11, 1997 to Cole et al discloses an aircraft propulsive power unit having a forward nacelle portion that is translatable fore and aft on side rails mounted on the exterior of the acoustic intake barrel that is secured to the engine fan case. Pins are provided to lock a nose lip portion of the forward nacelle portion to a flange located at the leading edge of the acoustic intake barrel.
U.S. Pat. No. 5,035,379 issued on Jul. 30, 1991 to Hersen et al discloses a movable cowling for an unducted aircraft turbine engine having a stationary fairing portion attached to an engine support pylon and a movable cowling portion. The movable cowling portion is provided with a slotted portion to accommodate a stationary fairing portion secured to the engine and to the pylon. A telescoping beam is attached to the engine and to the movable cowling portion to permit the cowling to be translated forwardly from a closed engine enclosing position to an open position to uncover the engine.
U.S. Pat. No. 5,941,061 issued on Aug. 24, 1999 to Sherry et al discloses an aircraft propulsive power unit having a bifurcated forward nacelle portion that is hingedly secured to an elongated pylon portion. The two piece forward nacelle portion is provided with a leading edge lipskin that cooperates with the forwardly extending end of an annular acoustic air inlet to provide an integral nose cowl and fan cowl portion when the bifurcated portions are lowered and locked into cooperation with the acoustic inlet.
U.S. Pat. No. 5,372,338 issued on Dec. 13, 1994 to Carlin discloses a nacelle of a gas turbine engine that is attached to an aircraft wing by a pylon. The nacelle is split horizontally to form a pair of opposing arcuate doors which are moveable between and open and closed positions. When the doors are closed a ring on the fan casing locates in a correspondingly shaped groove on the inner surface of the arcuate doors for the purpose of integrating the fan casing with the ring and sharing engine loads through the nacelle structure.
U.S. Pat. No. 5,603,471 issued Feb. 18, 1997 to Armstrong discloses a ducted fan turbine engine nozzle assembly. The thrust reverser portion of the nacelle and a portion of the discharge nozzle are integrated into a bifurcated door arrangement that is hinged to the pylon for pivoting movement between and an open position and a closed, operational position. Locators cooperate with the bifurcated doors to permit transmission of flight loads through the nacelle.
Although many such advances are noteworthy to one extent or another, none achieves the objectives of the present invention to provide an independently mounted translatable air inlet system for a turbofan aircraft jet engine.
It is a general object of this invention to provide an independently mounted translatable air inlet system for a turbofan aircraft jet engine that reduces the bending moment imposed on the fan case of the engine during certain flight conditions.
It is a further general object to reduce the weight and simplify the construction of an air inlet system for a turbofan aircraft jet engine.
It is a specific object of this invention to provide an independently mounted translatable air inlet system for a turbofan aircraft engine that provides a stable but flexible interface between the acoustically treated inner barrel of the inlet and the fan case of the engine.
The foregoing has outlined some of the more pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.
In accordance with the invention, an aircraft propulsion system arrangement is provided to reduce or eliminate inlet cowl induced bending of an aircraft jet engine case during certain flight conditions. This arrangement comprises a turbofan aircraft jet engine having an engine case with a fan case portion, a nacelle structure housing the engine and having a forward generally cylindrical nacelle portion and a rearward nacelle portion and a pylon structure to support the engine and the forward nacelle structure portion while permitting relative movement between the forward and rearward nacelle portions. The pylon structure supports the forward nacelle portion independently of its support of the engine while permitting translational movement of the forward nacelle portion on the pylon structure from a locked operational position during operation of the engine to a forward servicing position during non-operation of the engine. The forward nacelle portion provides an air inlet cowl portion directly coupled to the fan case portion of the engine for supply of air to the engine and a fan housing portion which surrounds the fan case portion of the engine. The forward nacelle portion includes a noselip portion having an inner main skin which extends rearwardly to sealingly engage the fan case portion of the engine and an outer generally concentric main skin which extends rearwardly to lockingly engage the rearward nacelle portion. In the forward servicing position of the forward nacelle portion it may be spaced forwardly from said fan case portion of the engine to uncover the outer fan case portion of the engine to give access to the engine and to components mounted on the engine which are inaccessible when the forward nacelle portion is secured in the operational position.
An extensible track arrangement is provided to permit determinable translation of the forward nacelle portion between a locked operational position during operation of the engine and a forward servicing position. A screw jack arrangement is determinably actuable to extend and retract the extensible track arrangement to translate the forward nacelle portion. Actuable locking means provide locking of the aft end of the outer skin of the forward nacelle portion to a forward flange means of the rearward nacelle portion. A suitable seal means such as a groove and blade arrangement provides a non-locking sealing and limited loading engagement between the aft end of the inner main skin of the forward nacelle portion and an annular flange provided on the fan case portion of the engine.
The foregoing has outlined rather broadly the more pertinent and important features of the present invention in order that the detailed description of the invention that follows may be better understood so that the present contribution to the art may be more fully appreciated. Additional features of the invention will be described hereinafter which form the subjects of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the disclosed specific embodiment may be readily utilized as a basis for modifying or design in other structures and methods for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions and methods do not depart from the spirit and scope of the invention as set forth in the appended claims.